The present invention relates to semiconductor materials having enhanced thermoelectric properties for use in fabricating thermoelectric devices and more particularly, to a thermoelectric device having co-extruded P-type and N-type material.
The basic theory and operation of thermoelectric devices has been developed for many years. Presently available thermoelectric devices used for cooling typically include an array of thermocouples which operate in accordance with the Peltier effect. Thermoelectric devices may also be used for heating, power generation and temperature sensing.
Thermoelectric devices may be described as essentially small heat pumps which follow the laws of thermodynamics in the same manner as mechanical heat pumps, refrigerators, or any other apparatus used to transfer heat energy. A principal difference is that thermoelectric devices function with solid state electrical components (thermoelectric elements or thermocouples) as compared to more traditional mechanical/fluid heating and cooling components. The efficiency of a thermoelectric device is generally limited to its associated Carnot cycle efficiency reduced by a factor which is dependent upon the thermoelectric figure of merit (ZT) of materials used in fabrication of the associated thermoelectric elements. Materials used to fabricate other components such as electrical connections, hot plates and cold plates may also affect the overall efficiency of the resulting thermoelectric device.
Thermoelectric materials such as alloys of Bi2Te3, PbTe and BiSb were developed thirty to forty years ago. More recently, semiconductor alloys such as SiGe have been used in the fabrication of thermoelectric devices. Commercially available thermoelectric materials are generally limited to use in a temperature range between 200 K and 1300 K with a maximum ZT value of approximately one. Typically, a thermoelectric device incorporates both a P-type semiconductor and an N-type semiconductor alloy as the thermoelectric materials.
In order to manufacture a thermoelectric device, a billet of P-type material is extruded to form a P-type extrusion. Similarly, a billet of N-type material is extruded to form an N-type extrusion. The P and N-type extrusions are sliced into wafers, the wafers are sliced into elements, and the elements are mechanically loaded into a grid or xe2x80x9cmatrixxe2x80x9d with the desired pattern and assembled upon a plate. P-type and N-type elements are typically arranged into rectangular arrays, in order to form a thermoelectric device. P-type and N-type legs alternate in both array directions. A metalization may be applied to the P-type wafers, N-type wafers, and/or the plate, in order to arrange the P-type wafers and the N-type wafers electrically in series and thermally in parallel.
For many thermoelectric devices, the elements dimensions are approximately 0.6 mm by 1.0 mm. Generally, the legs have a square cross-section perpendicular to the direction of current flow. Commonly, there are 18 to 36 pairs of P-type and N-type elements. Due to the size of the P-type and N-type elements, the elements are typically separated using a vibe loader for installation upon the plate according to a predetermined generally alternating pattern. This method is time-consuming and intricate, and requires specialized equipment and experienced operators.
In accordance with teachings of the present invention, the design and preparation of semiconductor materials for fabrication of thermoelectric devices has been substantially improved to provide enhanced manufacturing and operating efficiencies. More specifically, a billet including P-type material and N-type material is extruded in order to form an extrusion having both P-type regions and N-type regions. Accordingly, the extrusion may be sliced into wafers and processed for assembly of thermoelectric circuits and/or thermoelectric devices.
In accordance with the particular embodiment of the present invention, a method for forming a thermoelectric material includes combining at least one P-type extrusion with at least one N-type extrusion to form a first P/N-type billet. The P/N-type billet may be extruded to form a first P/N-type extrusion having at least one P-type region, and at least one N-type region. In a particular embodiment, the number of P-type regions and N-type regions may correspond to the number of P-type extrusions and N-type extrusions used to form the P/N-type billet.
In accordance with another embodiment of the present invention, the number of P-type regions and N-type regions may be unequal. However, depending upon the particular application and the desired end product, the number of P-type regions and N-type regions may be equal.
In accordance with yet another embodiment of the present invention, the P/N-type extrusion may be sliced in order to form wafers. The wafers may be metalized in order to couple the P-type regions and N-type regions electrically in series, and thermally in parallel.
Technical advantages of particular embodiments of the present invention include an extrusion having a predetermined number of P-type regions and a predetermined number of N-type regions. Accordingly, the extrusion may be sliced, processed, and assembled upon a plate in order to form a thermoelectric device. Assembly, therefore, does not require vibe loading and/or separation of individual P-type and N-type elements prior to assembly.
Another technical advantage of particular embodiments includes a method for forming an extrusion having a predetermined number of p-type regions and a predetermined number of N-type regions, arranged according to a predetermined configuration. Therefore, an extrusion may be formed to suit the particular application, and desired end product simplifying the assembly of a thermoelectric device.